Quick questions on Solubility equilibria and Ksp: WACE Year 12 Chemistry

The molar solubility is the number of moles of the salt that dissolve per litre to give a saturated solution. You can convert between $K_{sp}$ and solubility using the stoichiometry of the dissolving equation. If the molar solubility of $\text{CaF}_2$ is $s$, then $[\text{Ca}^{2+}] = s$ and $[\text{F}^-] = 2s$, so $K_{sp} = s(2s)^2 = 4s^3$.

When two solutions are mixed, you decide whether a precipitate forms by calculating the ionic product $Q$ (the same form as $K_{sp}$ but using the actual mixed concentrations) and comparing it with $K_{sp}$.